ABSTRACT Only 3-20% of people with eating disorders (EDs) receive treatment, and they often do not receive evidence- based treatments because they are intensive and costly, and few clinicians deliver them. These factors have hindered broad implementation, implying that a brief frontline outpatient treatment for a range of EDs that could be easily, cheaply, and widely implemented would address a key public health problem. There are also limited experimental data regarding factors that maintain EDs and mechanisms of action for ED treatments. We hypothesize that EDs are maintained by (1) excessive valuation of the thin ideal, which prompts caloric restriction and other unhealthy weight control behaviors (vomiting, laxative/diuretic use, excessive exercise) that increase risk for binge eating, and (2) excessive valuation of high-calorie foods, which maintains binge eating. We propose to evaluate a group treatment that efficiently targets these 2 maintenance factors. We created a novel 8-session dissonance-based treatment (Counter Attitudinal Therapy; CAT) wherein women with any ED complete verbal, written, and behavioral activities in which they discuss costs of pursuing the thin ideal and the ED behaviors they use to purse this ideal, which putatively creates dissonance about engaging in these behaviors that reduces valuation of the thin ideal and high-calorie binge foods. In two pilot trials CAT reduced behaviorally-assessed valuation of thin models and binge foods, and blinded interviewer-assessed ED symptoms versus unstandardized (d=.94) and standardized usual care (d=.53), resulting in a 70% remission by 2-6 month follow-up across the two trials. Effect sizes compare favorably to those produced by 20-session individual therapies for EDs. Women who completed the dissonance-inducing activities regarding pursuit of the thin ideal showed a reduction in fMRI-assessed reward region response to thin models (Stice et al., 2015) providing further evidence of target engagement. The R61 randomized trial (N=60) will (1) validate whether CAT produces larger pre-post reductions in objective fMRI-assessed reward region response to thin models and binge foods (intervention target measures) versus waitlist controls in women with DSM-5 EDs; (2) generate preliminary data regarding the clinical effects of reducing the targets on ED symptom domains and functioning (outcomes); and (3) test whether reductions in targets and outcomes show a linear decrease over the 8 sessions or plateau earlier and correlate with greater session attendance and homework completion, to examine dose-response relations. If the R61 confirms that CAT sufficiently engages intervention targets and that the 8-session format produces optimal response, the fully-powered R33 randomized trial (N=120) will test whether (4) CAT produces greater reductions in the two fMRI-assessed targets than a usual care group treatment; (5) CAT produces greater reductions in ED symptoms and functional impairment than the usual care treatment through 6-month follow-up; and (6) change in targets correlates with change in ED symptoms and functioning, and mediates intervention effects on outcomes.